Finding a substrate material for solar cells that simultaneously provides a high optical transparency and a high transmission haze is challenging. It now appears that an engineered paper could be an ideal substrate. Scientists have developed a wood-fibre-based nanostructured paper that provides a transparency of ~96% and a haze of ~60%. This material is potentially useful for photo-voltaics, where it could reduce the angular dependence of light harvesting for solar cells, and it could also benefit outdoor displays by reducing glare and specular reflections of sunlight. (Initial demonstration can be seen in Nano Lett.14, 765–773; 2014).

The team produced the transparent paper by using an oxidation process called TEMPO to introduce carboxyl groups into the cellulose fibres of wood. This process weakens the hydrogen bonds between the cellulose fibrils, causing the wood fibres to swell. The result is a paper with a much higher packing density than usual and greatly improved optical transparency and haze.

Analysis by scanning electron microscopy revealed that the transparent paper has a homogenous surface as a result of voids being filled by small fibre fragments. In the spectral range of 400–1,100 nm, the transparent paper had a transmittance of ~96% and a transmission haze of ~60%.

The benefits of the enhanced haze of the transparent paper for photo-voltaic devices were demonstrated by laminating the paper to the top of an organic solar cell and measuring the cell’s photo-current as a function of the incident angle of white light.

According to the authors, the improvements can be explained by two factors i.e. the reduced reflection of the light due to the low index contrast between the top layer of the photo-voltaic device and the transparent paper, and the directional change of the incident light in the transparent paper.

Scientists are pushing for further results regarding efficiency of Solar Cells by modifying them with paper developed using this technology. With promising initial results, can this technology will be helpful in decreasing the efficiency bottleneck of the Solar Cells – we have to wait.

Edited and Extracted from article by Noriaki Horiuchi in Nature (doi:10.1038/nphoton.2014.43)

“Implants that dissolve in the body after they’ve done their work could solve biocompatibility problem”

Researchers at the University of Illinois at Urbana-Champaign and Tufts University say they have invented functional electronic implants that can dissolve after programmable time periods. To demonstrate the system, which could aid in healing during the first few crucial days after an operation, they implanted one in a rat. It created a temporary temperature increase to sterilize a wound, and then it dissolved after 15 days. The researchers reported the development this week in the journal Science.

Biomedical researchers are turning to the idea of “programmable degradation” because it is difficult to develop materials that remain compatible with human tissue over the long term. Medical implants or drug-delivery systems that do their work and then disappear are ideal. To develop the electronic implants, the researchers encased them in silk. That material’s characteristics, particularly its crystallinity, can be adjusted so that its degradation time can be anywhere from seconds to years.

The electronics inside the silk were based on nanometers-thick sheets or ribbons of silicon, called silicon nanomembranes. The materials have been previously used to make experimental transistors, diodes, complementary logic devices, and photocells for flexible surfaces. Whereas a conventional silicon wafer or a chip would take about a thousand years to dissolve in biofluids, says John A. Rogers, who led the research at the University of Illinois, a nanomembrane is gone in a couple of weeks.

Working with the team at Illinois, Tufts researchers provided expertise on silk and carried out the animal experiments. Analytical modeling was done at Northwestern University in collaboration with Dalian University of Technology, in China, and a University of Arizona clinician identified the heat-therapy application.

While there have been no human trials yet, the component materials of the system are found in implants that have been approved by government regulators for other medical uses, Rogers points out. Silk is approved for sutures, magnesium is used for intravascular stents, and silicon is used for drug-delivery systems. “You have to do trials, because biology is complicated,” Rogers says, “but the materials are not complicated.”

The researchers tested a host of such transient components like inductors, capacitors, resistors, diodes, and transistors. All the components disintegrated and dissolved when immersed in deionized water. The materials and fabrication techniques may be used to make components for electronic systems in complementary metal-oxide semiconductor (CMOS) logic.

“Here is this toolbox that you can make anything with,” says Christopher J. Bettinger, a biomaterials researcher at Carnegie Mellon University who was not involved in the research, adding that the work was a remarkable feat of integration that neatly combined pieces from several areas. It’s also a very flexible system, he says; for example, the silk substrate could be swapped with other biodegradable polymers.

Jeffrey Borenstein, a researcher at the Charles Stark Draper Laboratory in Massachusetts, was also impressed. “As a general demonstration, this is very powerful,” he says. “When it comes to specific applications, you will have to evaluate how each of these materials performs inside the body.”

One challenge ahead could be finding additional ways to power the implants. The first version was powered by RF energy, but RF coils “are just very sensitive to orientation,” Bettinger says, adding that if you have a patient who moves around, it might change the power requirements.

The Illinois researchers, however, might have something in their favor. There is a synergy, Rogers says, between their work and the multibillion-dollar semiconductor industry that isn’t immediately obvious. As with conventional CMOS devices, with transient electronics, thinner is better. “I think we will be able to bootstrap off of advances in conventional electronics,” he says.

Abstract
A remarkable feature of modern silicon electronics is its ability to remain physically invariant, almost indefinitely for practical purposes. Although this characteristic is a hallmark of applications of integrated circuits that exist today, there might be opportunities for systems that offer the opposite behavior, such as implantable devices that function for medically useful time frames but then completely disappear via resorption by the body. We report a set of materials, manufacturing schemes, device components, and theoretical design tools for a silicon-based complementary metal oxide semiconductor (CMOS) technology that has this type of transient behavior, together with integrated sensors, actuators, power supply systems, and wireless control strategies. An implantable transient device that acts as a programmable nonantibiotic bacteriocide provides a system-level example.

Abstract
Many existing and envisioned classes of implantable biomedical devices require high performance electronics/sensors. An approach that avoids some of the longer term challenges in biocompatibility involves a construction in which some parts or all of the system resorbs in the body over time. This paper describes strategies for integrating single crystalline silicon electronics, where the silicon is in the form of nanomembranes, onto water soluble and biocompatible silk substrates. Electrical, bending, water dissolution, and animal toxicity studies suggest that this approach might provide many opportunities for future biomedical devices and clinical applications.

Electronics that dissolve in water could be used for medical implants and for biodegradable gadgets.

Today’s the kind of day when you can see the future. Today, the U.S. Food and Drug Administration (FDA) approved the first treatment that can restore (limited) eyesight to (some) blind people. Despite the caveats, it’s an exciting milestone.

The treatment involves electrodes implanted in the eyes of people whose retinas are damaged. The FDA approved the implants for people with severe cases of retinitis pigmentosa, a relatively small patient population. But the company that makes the implants, Second Sight Medical Products, says they can benefit a much broader group of people with vision problems, including many elderly people who suffer from macular degeneration.

IEEE Spectrum covered the technology in “Birth of the Bionic Eye.” One of the test subject, Barbara Campbell (pictured).

That article was part of the “Top Tech 2012” special report based on Second Sight’s optimistic predictions that it would win FDA approval for the implants in the year 2012. So the company is a couple of months behind schedule in the United States, but its implants have been on the market in Europe since 2011.

Second Sight isn’t the only company working on retinal prostheses.They have also described a competing technology from the German company Retina Implant AG, whose system was undergoing clinical trials last year.

Fifteen-year-old Jack Andraka recently won the world’s largest high school science competition for his development of a new, cheap and accurate test for detecting pancreatic cancer.
[Note: We want you to see these talks exactly as they happened! The archive footage might be a little rougher than the usual TED.com talk.]

What if you could plant a listening device in a single cancer cell, a bug that would follow the cell’s movements, eavesdrop on its metabolism and tell you what it’s up to?

A group of Stanford University researchers has made a start with a minuscule optical-cavity splinter small enough to insert in single cells and light enough remain embedded as the cells move about and multiply.

Gary Shambat and colleagues in Jelena Vuckovic’s Nanoscale and Quantum Photonics Lab built up a gallium arsenide wafer studded with three layers of indium arsenide quantum dots. They then etched away the supporting substrate, leaving a tapering, 200-micrometer-long beam tipped with a blade 20 micrometers long, 400 to 650 nanometers wide, and 220 nanometers thick. The business end of the blade looks like a strut from an infinitesimal Meccano Erector set: it’s pierced by 20 holes (averaging 120 nm across, though their diameters and spacing diminish towards the tip); five of the holes constitute an optical cavity, a hall of mirrors that resonates at a wavelength close to the quantum dots’ 1350 nm photoluminescence.

Like so many ultra-small optical devices, the nanocavity probe’s resonant frequency changes when molecules from its environment adhere to the beam’s surface. In this case, the emitted light shifts about 6 nm to the red for every 10 nm of film thickness. In a properly constructed assay, the thickness of the film will be a function of the specific substances sticking to the probe.

Shambat, Vuckovic, and their collaborators demonstrated this phenomenon by accurately detecting the binding of streptavidin (a protein produced by Streptomyces) to biotin (vitamin B7). (The binding between the two molecules is extraordinarily strong, and serves as the foundation of countless bioassays.) The researchers coated the nanoprobe with biotin. They found that random binding of streptavidin to the probe prompted a 0.5 nm red shift, while the stronger biotin-streptavidin binding produced shifted the luminescence peak by 3.5 nm.

When further developed, the device could offer an additional tool in the increasingly important study of single living cells. “Let’s say you have a study that is interested in whether a certain drug produces or inhibits a specific protein. Our biosensor would tell definitively if the drug was working, and how well, based on the color of the light from the probe. It would be a powerful tool,” said co-author Sanjiv Sam Gambhir, chair of the Stanford Medical School radiology department.

Detecting rare pathological cells is of obvious clinical significance. Sensitive and selective RGO-based electrochemical biosensors were developed and demonstrated in literature to detect cancer cells with over expressed nucleolin on plasma membrane (e.g. breast cancer cells and human cervical carcinoma cells), at a LOD of thousand cells per ml.

To avoid RGO aggregation and introduce more –COOH groups, 3,4,9,10-perylene tetracarboxylic acid (PTCA) was used as a composite with RGO. The nanocomposite was covalently functionalized with NH2-modified nucleolin-specific aptamers (oligonucleotides serving as highly selective antibodies) as the recognition element. The binding of cancer cells increases the electron transfer resistance by blocking the access of the redox probe ([Fe(CN)6] 3-/ 4-). Electrochemical detection in amperometry mode provides high temporal resolution (milliseconds). Therefore, it is suitable to detect dynamic cellular activities in real-time.

A RGO based sensor for detection of the real-time kinetics of oxygen release from human erythrocytes in response to NaNO2 stimulation has been shown. Two kinds of excellent mediators for O2 reduction, namely, laccase (Lac) and 2,2-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS), were functionalized onto RGO sheets to form a Lac–ABTS–RGO hybrid electrode.

An O2 level as low as 10 mM can be detected by this hybrid electrode. Cellular release of reactive oxygen species (such as H2O2) is an early indicator for cytotoxic events and cellular disorders. A RGO based electrochemical sensor has been coupled with live human breast cancer cells (MCF-7) to detect triggered cellular release of H2O2 in real-time and with a LOD of 0.1 mM.

To construct the electrode, RGO sheets were first electro-phoretically deposited on the indium tin oxide (ITO) glass. This was followed by electro-deposition of Prussian blue (artificial H2O2 catalyst) and adsorption of extracellular matrix proteins (laminin) to promote cell adhesion. Ten layers of RGO–PB–laminin were formed on the ITO substrate using layer-by-layer deposition. In situ, real-time, sensitive, and quantitative detection of extracellular H2O2 release from live cells was demonstrated. Specifically, it was determined that, upon stimulation of phorbol-12-myristate-13-acetate (PMA, 5 mg ml-1), 1011 H2O2 molecules were released from a single MCF-7 cell over 25 s.

Extracted and edited from “Biological and chemical sensors based on graphene materials by Yuxin Liu, Xiaochen Dong and Peng Chen in Chemical Society Reviews, 2012″